By: Yiwei Shang

Hi everyone! My name is Yiwei Shang, I’m a second-year PhD student in Dr. Sergio Sañudo-Wilhelmy’s Lab at USC and a 2021 Wrigley Summer Fellow. I study the distribution of various B vitamins in global surface ocean, and their potential role in regulating the phytoplankton groups.

B vitamins are required in the most important central metabolic pathways in all life forms, and they are a limiting factor that regulates the community structure and biomass of marine microbes, especially in primary producers. Despite the well-known biological and ecological relevance of the B vitamins, the ambient stability and decomposition products of these vital metabolites in the marine environment remains elusive.

Fig. 1. Happy sea day at USC Wrigley!

Based on Wrigley Summer Fellowship project, I sought to answer these fundamental questions: For B vitamins in the ocean, do they have ‘best-before date’ (their persistence in seawater)? Will they get ‘sunburned’ (the impact of sunlight on their stability and chemical transformations)? It is only possible to address those complex questions by carrying out a large-volume and full-factorial incubation experiment, and USC Wrigley provides an ideal setting to conduct a bioassay experiment of this scale.

Fig. 2. Preparation of the B-vitamin’s spiking solution

40 liters of surface seawater was collected at SPOT (San Pedro Ocean Time-series) during R/V Yellowfin’s May cruise (many thanks to Troy), with the proper filtration and autoclaving, any biotic or abiotic factors will be ruled out at this step. Following that, we make B vitamins’ spiking solutions in our lab at USC main campus, vitamin B1, B7, B12 and the congeners of B1 (Thiamin monophosphate, TMP; Thiamin pyrophosphate, TPP; 4-amino-5-hydroxymethyl-2- methylpyrimidine, HMP) and B12 (Cyanocobalamin, CB12; Hydroxycobalamin, HB12; Adenosylcobalamin, AB12; Methylcobalamin, MB12) were included in the experiment (see Fig. 2.)

Fig. 3. Overview of experimental design

A 4-week long incubation experiment is designed to use the large-volume incubation system at the Wrigley campus. The experiment was set under ambient temperatures and light levels (day/night cycle) mimicking the environmental conditions of the surface ocean. Samples will be collected at different intervals of time (from hours, days to weeks) to establish, for the first time, the temporal changes of vitamin B1, B7, B12 concentrations and their chemical congeners. For sample measurement, I will rely on new protocols combine a preconcentration step and quantification using a state-of-the-art LC-MS-MS (Fig. 3.). This project will then identify the decomposition products as well as to examine the B vitamins’ bioavailability time in seawater.

Fig. 4. Incubation setup at the Wrigley campus

B vitamins were undetectable in large areas of the coastal ocean, resulting the so-called Vitamin ‘Deserts’, which will eventually limit the growth and primary production of phytoplankton. This depletion can be attributed to a net outcome of the production and consumption of various B vitamins in relate to the biological activity. However, it also can be related to the persistence and stability of B vitamin as a chemical compound in the surface ocean. Based on the preliminary results generated from my first round of analysis, at least B12, has a short bioavailability time with only 1.25 day of half-time, suggests a rapid cycling of this organic metabolite in the surface ocean. Overall, this study will give us a new piece of evidence that explains why B vitamins are so depleted in the ocean.

Fig. 5. Iconic view on Catalina Island

Last but not least, I want to take this opportunity to thank all the faculty and staff members in the USC Wrigley Institute for hosting me and helping me throughout the experiment, as well as the support from the Sañudo Lab. This work is funded by the Wrigley Institute Summer Fellowship. I look forward to conducting research on the beautiful Catalina Island again in the near future!